1. Field of the Invention
The present invention relates generally to communication systems and methods, and more particularly, to an exciter which can generate a communication band low-noise signal.
2. State of the Art:
Communication systems which employ wireless transceivers are well known. However, as is the case with most electronic technologies today, there is an ever increasing demand to improve information transmission rates and range (that is, power output), while at the same time, reducing the influence of noise and improving the quality of transmission. In addition, there is always increasing demand to broaden the applicability of wireless communications to technologies still dependent on wired or fiber linked communication, such as mainframe-to-mainframe communications where high data rate and high power requirements have precluded the use of conventional wireless communications. To satisfy these competing concerns, a compromise is often reached whereby some sacrifice in transmission rate is accepted to enhance the integrity of the data transmitted. In addition, some sacrifice in transmission range is accepted to reduce the transceiver""s circuit complexity and cost.
One feature of conventional communication systems which affects information transmission rates and range is the exciter used for information transmission and reception. Although a wide variety of exciters are known for general information transmission/reception, the availability of exciters appropriate for use in high power, high transmission rate systems is limited. Moreover, the exciters which may be useful for such applications do not exhibit high phase-noise performance or, can only achieve an acceptable phase-noise performance characteristic using a high cost, complex exciter circuit arrangement which would be impractical from size and cost efficiency standpoints.
Accordingly, it would be desirable to provide an apparatus and method for generating a communication band low-noise signal using a simplistic, cost effective approach that can satisfy system constraints of high power (e.g., on the order of 0.5 to 2 watts (W) or higher), high signal-to-noise (S/N) ratio, accommodate operating frequencies on the order of 18-40 Gigahertz (GHz) spectrums or wider, and actual transmission rates on the order of 100 to 125 Megabits per second (125 Mb/s), or higher.
The present invention is directed to providing a local oscillator suitable for use in a communication system capable of providing actual wireless transmission rates on the order of 125 Mb/s, or higher, with relatively high transmission power on the order of 0.5 to 2 watts (W) or higher, with a high signal-to-noise(S/N) ratio, a bit error rate on the order of 10xe2x88x9212 or lower, 99.99% availability, and with relatively simple circuit designs. Exemplary embodiments can provide these features using a compact and efficient, low distortion local oscillator for use in a transceiver design based on high power (e.g., 0.5 W) monolithic millimeter wave integrated circuits (MMICs), having a compression point which accommodates high speed modems such as OC-3 and 100 Mb/s Fast Ethernet modems used in broadband networking technologies like SONET/SDH (e.g., SONET ring architectures having self-healing ring capability). By applying high power MMIC technology of conventional radar systems to wireless duplex communications, significant advantages can be realized. Exemplary embodiments have transmit operating frequencies in a fixed wireless spectrum of 18-40 GHz or wider, and produce a power output on the order of 0.5 W to 2 W or more, with a relatively simple circuit design.
In addition, exemplary embodiments achieve a design compactness with an exciter design that can be employed for both the transmitter and receiver. As such, the present invention has wide application including, for example, point-to-point wireless communications between computers, such as between personal computers, between computer networks and between mainframe computers, over broadband networks with high reliability.
Generally speaking, exemplary embodiments of the present invention are directed to a method and apparatus for generating a communication band low-phase noise signal, comprising: a voltage controlled oscillator for producing an output frequency from a reference frequency; and means for producing any one of multiple frequency outputs of at least approximately 18 GHz with an integrated phase noise of no greater than approximately xe2x88x9240 dB, each of said multiple frequency outputs being separated from an adjacent frequency by a channel step size of at least one MHZ.